The present invention relates to methods and apparatus for monitoring an electrically actuated tool. More specifically, it relates to a method and apparatus for monitoring the current flow to an electrically actuated tool and ensuring that the tool is operated correctly on each successive run by preventing recycling of the tool in the event that the current flow is outside an acceptable range. The phrase electrically actuated tool is defined broadly to include electrically energized tools for working rivets, interference-fit fasteners, and metal components for welding. Examples of electrically actuated tools which may be used with the present invention are found in U.S. Pat. Nos. 3,646,791; 3,704,506; 3,731,370; 3,824,824; and application Ser. No. 487,747, filed July 11, 1974, entitled "Method And Apparatus For Driving Interference-Fit Fasteners". The present invention may also be utilized with electromagnetic metal forming apparatus, induction heaters, and the like, which are energized by electrical energy. Moreover, the present invention may be utilized with any other tool whose performance depends on the maximum output level of any dynamic variable if the variable is measurable and can be converted to an analog voltage.
Generally, known methods and apparatus for monitoring metal working tools utilize mechanical inspection apparatus, e.g., a hand calibrator. Such manual inspection techniques necessarily delay operation and are often imprecise.
U.S. Pat. No. 3,452,565 (Caldwell) discloses means for controlling the voltage level desired for charging and discharging of a capacitor bank by employing relays and switches. Actuation of the switches opens the charging circuit to terminate charge build-up. Sequentially operated time delayed relays or a multi-cam motor actuator are employed to control charging and discharging to provide continuous operation. Such apparatus is concerned only with establishing a pre-set voltate value at the energy source, and not with monitoring the current flowing in the tool circuit to prevent recycling of the tool when the current flow to the tool is not within an acceptable range.